The Hurricane & Storm Damage Risk Reduction System (HSDRRS) is a flood protection system in southern Louisiana that helps protect the Greater New Orleans area from storm surges. It is designed to reduce the risk of flooding to a level that would occur once every 100 years, meaning there is a 1% chance each year that a storm surge of that size or larger could happen. In 2019, the U.S. Army Corps of Engineers reported that rising sea levels and sinking land could lower the system’s ability to protect against flooding by 2023.
History
After Hurricane Katrina in 2005, Congress approved and provided money for the construction of a new system to reduce risk from hurricanes and storms. This system, called the Hurricane and Storm Damage Risk Reduction System (HSDRRS), covers five parishes: Orleans, Jefferson, St. Bernard, St. Charles, and Plaquemines. It includes 350 miles of levees and floodwalls, 73 non-Federal pumping stations, 3 canal closure structures with pumps, and 4 gated outlets.
The Greater New Orleans HSDRRS is designed to reduce risk from tropical storms and related rainfall and storm surges to the level expected once every 100 years. The $14 billion system includes the construction or improvement of 133 miles of perimeter features, such as levees, floodwalls, floodgates, and pump stations. The system was designed to last 50 years and accounts for rising sea levels, land sinking, and more frequent storms during that time. Features to improve resilience include protecting the backside of levees and floodwalls to prevent erosion from waves.
The U.S. Army Corps of Engineers also supports a strategy with multiple layers of defense to reduce risk. This includes restoring coastal areas in Louisiana. Coastal habitats act as a natural buffer between open water and structures like the HSDRRS.
Construction
The HSDRRS was created quickly by the U.S. Army Corps of Engineers' New Orleans District, part of the Mississippi Valley Division. The program included more than 70 projects and used a method that combined design and construction to meet deadlines after Hurricane Katrina. Key parts of the system are 133 miles (214 kilometers) of perimeter levees and floodwalls, three canal closure structures with pumps, and the Permanent Canal Closures and Pumps system.
Experts from other countries helped plan and design the system. Dutch engineering companies like Arcadis, Royal HaskoningDHV, Fugro, and HKV Consultants worked on ideas for surge barriers, soil testing, and ways to make the system stronger.
The system includes features to help it stay strong, such as protecting the backside of levees and floodwalls to stop erosion when water flows over them. Construction was finished in 2018, and the total cost was about $14 billion.
Operation and maintenance
After the project was completed, the U.S. Army Corps of Engineers gave responsibility for operating and maintaining the system to local groups, such as the Southeast Louisiana Flood Protection Authority-East, Flood Protection Authority-West, and county levee districts. These groups use guides from the Corps to care for levees, floodwalls, gates, and pumping stations. They follow instructions for inspections and emergency actions. Money for maintenance comes from local property taxes and help from the state through the Coastal Protection and Restoration Authority. Each year, the cost of upkeep is expected to be in the tens of millions of dollars.
Future challenges
The Hurricane & Storm Damage Risk Reduction System must deal with long-term problems caused by rising sea levels and land sinking. Research shows that some levees and floodwalls are sinking by up to 28 millimeters each year—almost ten times faster than the global rise in sea levels. This sinking weakens their ability to protect against storm surges.
To keep the system’s protection level for 100 years, the U.S. Army Corps of Engineers plans regular “levee lifts” to raise levee heights as the ground settles. A 2023 report said that keeping the system working will need several lifts over 50 years, costing about $3.5 billion. This cost will be shared by 65% federal funding and 35% from other sources.
Climate change is expected to make hurricanes stronger and increase rainfall, adding more pressure on the system. Without updates, lower levee heights could make New Orleans more likely to flood and could affect eligibility for federal flood insurance programs.
Inner Harbor Navigation Canal Lake Borgne Surge Barrier
The IHNC Surge Barrier links the flood protection system in New Orleans East to the system in St. Bernard Parish. It includes a 150 ft (46 m) sector gate, a 150 ft (46 m) barge gate along the Gulf Intracoastal Waterway, and a 1.8 mi (2.9 km) concrete floodwall. Completed in June 2013, it is the largest civil works project in Louisiana history. The total construction cost was approximately $1.1 billion.